In connection with the operation of diesel engines, the primary harmful substances that are emitted with the exhaust gases are NO.sub.x compounds. Efforts have been made to reduce the NO.sub.x content. For this purpose cooled exhaust gas is returned or fed back from the exhaust of the diesel engine to its fresh air supply. It has been determined that a return of about 20% of the exhaust gas volume reduces the NO.sub.x value to about one half of the value it would have without the exhaust gas return. The reduction of the NO.sub.x value can be seen as the result of the increased CO.sub.2 proportions in the combustion air where an exhaust gas return into the fresh air supply takes place. However, the just described exhaust gas return has the disadvantage that the soot content of the exhaust gas rises with an increase in the exhaust gas return into the fresh air supply. The result of the higher soot content on the other hand leads to an increased wear and tear of the diesel engine. Yet another disadvantage is seen in that the exhaust gas cooler is contaminated already after a short operational period.
German Patent Publication (DE-AS) 24 54 829 discloses a multicylinder internal combustion engine in which one cylinder which is intended for receiving exhaust gas, has a higher compression ratio than the other cylinders of the engine. The cylinder with the higher compression ratio is connected with its exhaust port to the inlet ports of the other cylinders. The higher compression ratio cylinder provides a drive power only during the starting of the internal combustion engine. During starting, a closure valve is closed in an exhaust pipe so that the cylinder with the higher compression ratio takes up the exhaust gases from the other cylinders and ignites these exhaust gases. During normal operation of the internal combustion engine the cylinder with the higher compression ratio takes up a portion of the exhaust gases of the other cylinders, thereby dosing that portion and cooling it. This prior art device for an exhaust gas return is structurally involved and hence its manufacture is expensive.
German Patent Publication (DE-OS) 39 30 243 discloses a multicylinder internal combustion engine with a fresh air suction intake and with a collection system for the exhaust gases, including an exhaust gas return device for the reduction of harmful substances in the exhaust. In order to operate the internal combustion engine of the just mentioned German Patent publication with an exhaust gas turbo-charger and with a fresh air cooler, the exhaust gas return device comprises an exhaust gas distributor. This exhaust gas distributor has branching end pipes, the number of which corresponds to the number of the cylinders in the internal combustion engine. The exhaust gas distributor is connected to the exhaust gas pipe of one cylinder while the exhaust gas pipes of the other cylinders are connected to an exhaust gas collector pipe. The end pipes of the exhaust gas distributor lead into the cylinder suction intake pipes directly or immediately upstream of the inlet valve of the respective cylinder. The problem of an increased soot concentration has not been solved by the just mentioned apparatus. The increased soot concentration in the returned exhaust gas and the above mentioned disadvantages caused thereby for the internal combustion engine and the emission of more soot still poses a problem that leaves room for improvement.